Fixing Singleton typing to correctly return child class (#1914)

- Add distinction between `getInstance` and `getInstanceOrCreate` since
  it is not always possible to create an instance (since you might not
  know the correct arguments)

- Remove all the `export const *Store = *Store.getInstance<*Store>();`
  calls as it defeats the purpose of `Singleton`. Plus with the typing
  changes the appropriate `*Store.getInstance()` is "short enough".

- Special case the two extension export facades to not need to use
  `getInstanceOrCreate`. Plus since they are just facades it is always
  possible to create them.

- Move some other types to be also `Singleton`'s: ExtensionLoader,
  ExtensionDiscovery, ThemeStore, LocalizationStore, ...

- Fixed dev-run always using the same port with electron inspect

- Update Store documentation with new recommendations about creating
  instances of singletons

- Fix all unit tests to create their dependent singletons

Signed-off-by: Sebastian Malton <sebastian@malton.name>

.eslintrc.js

@@ -79,6 +79,8 @@ module.exports = {
         sourceType: "module",
       },
       rules: {
+        "no-invalid-this": "off",
+        "@typescript-eslint/no-invalid-this": ["error"],
         "@typescript-eslint/explicit-function-return-type": "off",
         "@typescript-eslint/no-explicit-any": "off",
         "@typescript-eslint/explicit-module-boundary-types": "off",
@@ -137,6 +139,8 @@ module.exports = {
         jsx: true,
       },
       rules: {
+        "no-invalid-this": "off",
+        "@typescript-eslint/no-invalid-this": ["error"],
         "@typescript-eslint/explicit-function-return-type": "off",
         "@typescript-eslint/no-explicit-any": "off",
         "@typescript-eslint/interface-name-prefix": "off",